The present invention relates to a scroll fluid machine suitable for use to compress a fluid, e.g. air.
In a generally known twin wrap type scroll fluid machine, two pairs of fixed and orbiting scroll members are provided respectively at two axial ends of a casing, and an electric motor for orbitally driving the two orbiting scroll members is provided in the casing (for example, see Japanese Patent Application Unexamined Publication (KOKAI). No. 2000-356193).
In this type of conventional twin wrap type scroll fluid machine, the fixed scroll member and the orbiting scroll member provided at one axial end of the casing form, in combination, compression chambers of a low-pressure stage, and the fixed scroll member and the orbiting scroll member provided at the other axial end of the casing form, in combination, compression chambers of a high-pressure, stage.
The fixed scroll member of the high-pressure stage is connected at its suction side to the discharge side of the fixed scroll member of the low-pressure stage by using piping or the like. Thus, a fluid compressed in and discharged from the compression chambers of the low-pressure stage is further compressed in the compression chambers of the high-pressure stage, thereby performing two-stage compression of the fluid.
Incidentally, in existing scroll fluid machines that perform two-stage compression as in the case of the above-described conventional twin wrap type, the fixed and orbiting scroll members are formed so that the radial gap formed between the respective wrap portions of the scroll members is minimized, and the radial gap of the low-pressure stage and the radial gap of the high-pressure stage are of approximately the same size.
The spiral wrap portions of the fixed and orbiting scroll members are formed from circumferentially extending plate-shaped walls, respectively. Each plate-shaped wall is subjected to heat generated by gas-compression effect when the fluid is compressed in the compression chambers. Consequently, a large temperature difference occurs between the inner and outer peripheral sides of the plate-shaped wall. Owing to the temperature gradient, the wrap portions are likely to be thermally deformed. Therefore, when the wrap portions are formed so that the radial gap therebetween is merely minimized, the wrap portions may contact or interfere with each other owing to the influence of thermal deformation. This causes degradation of reliability of the scroll fluid machine.
On the other hand, if the radial gap is increased to avoid contact or interference between the wrap portions, it becomes easy for the compressed fluid in the compression chambers to leak through the radial gap between the wrap portions. This makes it impossible to improve the performance of the scroll fluid machine.
In assembling a scroll compressor, it is necessary, when two scroll members are mated with each other, to adjust the position of each wrap portion with high accuracy so that the wrap portions will not contact or interfere with each other. In a scroll compressor having two different types of wrap portions for the high-pressure stage and the low-pressure stage, in particular, the position adjustment becomes even more difficult, and the number of man-hours needed to machine and assemble component parts increases unfavorably.
The present invention was made in view of the above-described problems with the prior art.
An object of the present invention is to provide a scroll fluid machine wherein the radial gap between the wrap portions in the low-pressure stage and that in the high pressure stage are made different from each other, thereby making it possible to reduce the influence of thermal deformation, minimize the leakage of fluid, improve the machine performance during compressing operation, etc. and reduce the number of man-hours needed to manufacture the scroll fluid machine.